1. Field of the Invention
This invention relates to the manufacture of soft, absorbent tissue paper webs and particularly to formulations for creping such webs to obtain improved softness in the web while increasing operational efficiency.
2. Description of the Related Art
The creping of paper webs by removing them from a heated surface, usually a rotating drum, with a doctor blade to impart softness to the web is well known in the art. The benefits and difficulties encountered in such a process have been extensively discussed in the prior art, notably, Grossman, U.S. Pat. No. 4,063,995, issued Dec. 20, 1977. The creping process depends upon controlling the adhesion of the web to the heated surface. Many adhesive formulations have heretofore been proposed. The present invention relates to creping adhesives which are applied to the creping drum, and more particularly to formulations comprising a water-soluble adhesive. See for example Grube et al, U.S. Pat. No. 4,304,625, issued Dec. 8, 1981, wherein the water soluble component is polyvinyl alcohol. The creping adhesive tends to coat the dryer with a hard and uneven film which builds up as drying and creping proceed, resulting in uneven creping and rapid wear of the creping blade itself. See Grube et al at Col. 2, lines 25-30. In many cases, a cleaning blade is used to scrape the film from the drum surface. These cleaning blades must be changed frequently. Additionally, they cause creping surface wear.
It has further been found that the addition of a phosphate salt to the creping adhesive formulation greatly reduces the problem of the hard film build-up on the creping surface. Chen et al, U.S. Pat. No. 4,883,564 issued Nov. 28, 1989. While the addition of a phosphate salt to the formulation reduced the need for changing blades and resulted in more even creping, practitioners have continued to desire greater heat stability of the creping adhesive, more tolerance of moisture variations in the paper web, longer crepe blade life and stronger adhesion of the paper web to the creping surface.